1. Field of the Invention
This invention relates to a liquid-jet head and a liquid-jet apparatus in which a part of a pressure generating chamber communicating with a nozzle orifice for ejection of liquid droplets is composed of a vibration plate, a piezoelectric element is formed on the vibration plate, and liquid droplets are ejected by displacement of the piezoelectric element. More particularly, the invention relates to an ink-jet recording head and an ink-jet recording apparatus for ejecting ink as a liquid.
2. Description of the Related Art
In an ink-jet recording head, a part of a pressure generating chamber communicating with a nozzle orifice for ejection of ink droplets is composed of a vibration plate, and the vibration plate is deformed by a piezoelectric element to pressurize ink in the pressure generating chamber, thereby ejecting ink droplets from the nozzle orifice. Two types of the ink-jet recording heads are put into practical use. One of them uses a piezoelectric actuator of a longitudinal vibration mode which expands and contracts in the axial direction of the piezoelectric element. The other uses a piezoelectric actuator of a flexural vibration mode.
The former type can change the volume of the pressure generating chamber by abutting the end surface of the piezoelectric element against the vibration plate, thus making it possible to manufacture a head suitable for high density printing. However, this necessitates a difficult process in which the piezoelectric element is cut and divided in a comb tooth shape coincident with the array pitch of the nozzle orifice, and an operation for aligning and fixing the cut and divided piezoelectric element to the pressure generating chamber. Thus, the problem arises that the manufacturing process is complicated. With the latter type, on the other hand, the piezoelectric element can be fabricated and installed on the vibration plate by a relatively simple process in which a green sheet, as a piezoelectric material, is affixed to the vibration plate in agreement with the shape of the pressure generating chamber, and is then sintered. However, a certain size of vibration plate is required due to the usage of flexural vibration, thus posing the problem that a high density array of the piezoelectric elements is difficult.
In order to solve the disadvantage of the latter recording head, a proposal has been made for a recording head in which a uniform piezoelectric material layer is formed across the entire surface of the vibration plate by a deposition technology, the piezoelectric material layer is cut and divided into a shape corresponding to the pressure generating chamber by a lithography method, and the piezoelectric element is formed so as to be independent of one another piezoelectric element for each pressure generating chamber. According to this process, the operation for affixing the piezoelectric element to the vibration plate is unnecessary. Moreover, the advantage is obtained that not only the piezoelectric element can be fabricated and installed in high density by the lithography method which is an accurate and simple method, but also the thickness of the piezoelectric element can be rendered small and a high speed drive can be accomplished.
With the ink-jet recording head having the piezoelectric elements arranged in a high density as described above, one of electrodes (i.e., a common electrode) of each piezoelectric element is formed to be common to the plurality of piezoelectric elements. Thus, when many of the piezoelectric elements are driven at the same time to eject many ink droplets at one time, the problem is presented that a drop in voltage occurs, leading to an unstable amount of displacement of the piezoelectric element and deteriorated ink ejection characteristics. To solve such a problem, a multi-layered electrode layer, a connecting wiring layer, etc., which comprise a conductive material, are provided on a lower electrode film which is the common electrode of the piezoelectric element. By so doing, it is attempted to lower the resistance value of the lower electrode film substantially, thereby preventing the occurrence of a drop in voltage (see, for example, Japanese Patent Application Laid-Open No. 2004-1431).
However, if the multi-layered electrode layer is directly formed on the lower electrode film, as in the structure described in the above patent document, there may be a problem such that stray current corrosion occurs between the lower electrode film and the multi-layered electrode layer in forming the multi-layered electrode layer.
Such a problem is not limited to the ink-jet recording head for ejecting ink, but also holds true of other liquid-jet heads for ejecting liquid droplets other than ink.